Control of switcher regulated power amplifier modules

ABSTRACT

Various embodiments described herein relate to a power management block and an amplification block used in the transmitter of a communication subsystem. The power management block provides improved control for the gain control signal provided to a pre-amplifier and the supply voltage provided to a power amplifier which are both in the amplification block. The power expended by the power amplifier is optimized by employing a continuous control method in which one or more feedback loops are employed to take into account various characteristics of the transmitter components and control values.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/784,971, filed May 21, 2010, which is a continuation of U.S. patentapplication Ser. No. 11/763,068, filed on Jun. 14, 2007, which claimsthe benefit of U.S. Provisional Application No. 60/813,352, filed onJun. 14, 2006. U.S. patent application Ser. No. 11/763,068 issued topatent as U.S. Pat. No. 7,907,920. The entire contents of applicationSer. No. 12/784,971, application Ser. No. 11/763,068 and of ApplicationNo. 60/813,352 are hereby incorporated by reference.

FIELD

This description relates generally to wireless communication devices andmore particularly to control of switcher regulated power amplifier usinginput drive.

BACKGROUND

Handheld wireless communication devices are powered by one or moreinternal batteries. A major performance criterion for such devices istheir battery life, and a large portion of battery power is consumed ina power amplification block of the device's transmitter. In manyhandheld wireless applications, a switched mode power supply, whichprovides the supply voltage to a power amplifier in the poweramplification block, is used to reduce overall power consumption.However, this requires careful control of the switched mode power supplyto achieve optimal power savings. In order to simplify control, manyconventional designs use a fixed-step, or continuous control techniquefor controlling the switched mode power supply. However, withoutemploying additional information, both of these techniques may result insub-optimal power savings, may be more cumbersome to calibrate, and mayhave an adverse affect on the output signal's compression artifacts.With most designs, the compression artifacts are very low compared tothe signal power until the supply voltage provided to the poweramplifier approaches its transmit power limit at which point thecompression artifacts increase.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the exemplary embodiments described hereinand to show more clearly how they may be carried into effect, referencewill now be made, by way of example only, to the accompanying drawingsin which:

FIG. 1 is a block diagram of an exemplary embodiment of a wirelesscommunications device;

FIG. 2 is a block diagram of an exemplary embodiment of a communicationsubsystem component of the mobile device of FIG. 1;

FIG. 3 is a block diagram of an exemplary embodiment of a portion of apower management block and an amplification block of the communicationssubsystem of the wireless communications device;

FIG. 4 is a flow chart diagram of an exemplary method that can be usedfor finding appropriate values for a switching control transfer functionfor a switch control block of the power management block; and

FIG. 5 is a block diagram of an exemplary embodiment of a power limitcontroller of the power management block.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where considered appropriate, reference numerals may be repeated amongthe figures to indicate corresponding or analogous elements. Inaddition, specific details may be included to provide a thoroughunderstanding of the embodiments described herein. However, it will beunderstood by those of ordinary skill in the art that the embodimentsdescribed herein may be practiced without these specific details. Inother instances, well-known methods, procedures and components have notbeen described in detail so as not to obscure the embodiments describedherein. Furthermore, this description is not to be considered aslimiting the scope of the embodiments described herein, but rather asmerely describing the implementation of the various embodimentsdescribed herein.

A wireless communications device is a two-way communications device withadvanced data communication capabilities having the capability tocommunicate with other computer systems. The wireless communicationsdevice may also include the capability for voice communications.Depending on the functionality provided by the wireless communicationsdevice, it may be referred to as a data messaging device, a two-waypager, a cellular telephone with data messaging capabilities, a wirelessInternet appliance, or a data communications device (with or withouttelephony capabilities). The wireless communications device communicateswith other devices through a network of transceiver stations.

Referring first to FIG. 1, shown therein is a block diagram of anexemplary embodiment of a wireless communications device 100 which mayalso be referred to as a mobile communications device. The wirelesscommunications device 100 comprises a number of components, such as acontrol unit 102 which controls the overall operation of the wirelesscommunications device 100. The control unit 102 may be a microprocessoror a microcontroller. Any commercially available microcontroller, suchas a microcontroller available from ARM, Motorola, Intel and the likemay be used for the control unit 102.

Communication functions, including data and possibly voicecommunications, are performed through the communication subsystem 104.The communication subsystem 104 receives messages from and sendsmessages to a wireless network 180. In one embodiment, the communicationsubsystem 104 may be configured in accordance with CDMA2000 standards,or with Global System for Mobile Communication (GSM) and General PacketRadio Services (GPRS) standards. The GSM/GPRS wireless network is usedworldwide and it is expected that these standards will eventually besuperseded by the Enhanced Data GSM Environment (EDGE) and UniversalMobile Telecommunications Service (UMTS) standards. New standards arestill being defined, but it is believed that they will have similaritiesto the network behaviour described herein, and it will also beunderstood that the device is intended to use any other suitablestandards that are developed in the future. The wireless link connectingthe communications subsystem 104 with the network 180 represents one ormore different Radio Frequency (RF) channels, operating according todefined protocols specified for CDMA2000 or GSM/GPRS communications.With the network protocols, these channels are capable of supportingboth circuit switched voice communications and packet switched datacommunications.

The control unit 102 also interacts with additional subsystems such as aRandom Access Memory (RAM) 106, a flash memory 108, a display 110, anauxiliary input/output (I/O) subsystem 112, a data port 114, a keyboard116, a speaker 118, a microphone 120, a short-range communicationssubsystem 122 and other device subsystems 124. Some of these componentsmay be optional depending on the particular type of wirelesscommunications device. Other types of non-volatile storage devices knownin the art may be used rather than the flash memory 108. The keyboard116 may be a telephone-type keypad, an alphanumeric keyboard or someother suitable keypad.

Some of the subsystems of the wireless communications device 100 performcommunication-related functions, whereas other subsystems may provide“resident” or on-device functions. By way of example, the display 110and the keyboard 116 may be used for both communication-relatedfunctions, such as entering a text message for transmission over thenetwork 180, and device-resident functions such as a calculator or tasklist. Operating system software, and other various algorithms, used bythe control unit 102 is typically stored in a persistent store such asthe flash memory 108, which may alternatively be a read-only memory(ROM) or similar storage element (not shown). Those skilled in the artwill appreciate that the operating system, specific device applications,or parts thereof, may be temporarily loaded into a volatile store suchas the RAM 106.

The wireless communications device 100 may send and receivecommunication signals over the network 180 after required networkregistration or activation procedures have been completed. Networkaccess is associated with a subscriber or user of the wirelesscommunications device 100. To identify a subscriber, the wirelesscommunications device 100 requires a Subscriber Identity Module or “SIM”card 126 or an R-UIM (Removable User Identity Module) to be inserted ina SIM interface 128 (or an R-UIM interface) in order to communicate withthe network 180. The SIM card or R-UIM 126 is one type of a conventional“smart card” that is used to identify a subscriber of the wirelesscommunications device 100 and to personalize the wireless communicationsdevice 100, among other things. Alternatively, user identificationinformation can also be programmed into flash memory 108. Services mayinclude: web browsing and messaging such as email, voice mail, ShortMessage Service (SMS), and Multimedia Messaging Services (MMS). Moreadvanced services may include: point of sale, field service and salesforce automation.

The wireless communications device 100 is a battery-powered device andincludes a battery interface 132 for receiving one or more rechargeablebatteries 130. The battery interface 132 is coupled to a regulator (notshown) which assists the battery 130 in providing supply power V+ to thewireless communications device 100. Although current technology makesuse of a battery, future power source technologies such as micro fuelcells may provide the power to the wireless communications device 100.

The control unit 102, in addition to its operating system functions,enables execution of software applications on the wirelesscommunications device 100. A set of applications which control basicdevice operations, including data and voice communication applicationswill normally be installed on the wireless communications device 100during its manufacture. Another application that may be loaded onto thewireless communications device 100 may be a personal information manager(PIM). A PIM has the ability to organize and manage data items ofinterest to a subscriber, such as, but not limited to, e-mail, calendarevents, voice mails, appointments, and task items. A PIM application hasthe ability to send and receive data items via the wireless network 180.In one embodiment, PIM data items are seamlessly integrated,synchronized, and updated via the wireless network 180 with the wirelesscommunications device subscriber's corresponding data items storedand/or associated with a host computer system. This functionalitycreates a mirrored host computer on the wireless communications device100 with respect to such items. This is especially advantageous wherethe host computer system is the wireless communications devicesubscriber's office computer system.

Additional applications may also be loaded onto the wirelesscommunications device 100 through the network 180, the auxiliary I/Osubsystem 112, the data port 114, the short-range communicationsubsystem 122, or any other suitable device subsystem 124. Thisflexibility in application installation increases the functionality ofthe wireless communications device 100 and may provide enhancedon-device functions, communication-related functions, or both. Forexample, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing the wireless communications device 100.

The data port 114 enables a subscriber to set preferences through anexternal device or software application and extends the capabilities ofthe mobile device 100 by providing for information or software downloadsto the mobile device 100 other than through a wireless communicationnetwork. The alternate download path may, for example, be used to loadan encryption key onto the mobile device 100 through a direct and thusreliable and trusted connection to provide secure device communication.

The short-range communication subsystem 122 provides for communicationbetween the wireless communications device 100 and different systems ordevices, without the use of the network 180. For example, the subsystem122 may include an infrared device and associated circuits andcomponents for short-range communication. Examples of short-rangecommunication may include standards developed by the Infrared DataAssociation (IrDA), Bluetooth, and the 802.11 family of standardsdeveloped by IEEE.

In use, a received signal such as a text message, an e-mail message, orweb page download will be processed by the communications subsystem 104and input to the control unit 102. The control unit 102 will thenprocess the received signal for output to the display 110 oralternatively to the auxiliary I/O subsystem 112. A subscriber may alsocompose data items, such as e-mail messages, for example, using thekeyboard 116 in conjunction with display 110 and possibly auxiliary I/Osubsystem 112. The auxiliary subsystem 112 may include devices such as:a touch screen, mouse, track ball, infrared fingerprint detector, or aroller wheel with dynamic button pressing capability. The keyboard 116may be an alphanumeric keyboard and/or telephone-type keypad. A composeditem may be transmitted over the network 150 through the communicationsubsystem 104.

For voice communications, the overall operation of the wirelesscommunications device 100 is substantially similar, except that most ofthe received signals are output to the speaker 118, and most of thesignals for transmission are transduced by microphone 120. Alternativevoice or audio I/O subsystems, such as a voice message recordingsubsystem, may also be implemented on the wireless communications device100. Although voice or audio signal output is accomplished primarilythrough the speaker 118, the display 110 may also be used to provideadditional information such as the identity of a calling party, durationof a voice call, or other voice call related information.

Referring now to FIG. 2, a block diagram of the communication subsystemcomponent 104 of FIG. 1 is shown. The communication subsystem 104comprises a receiver 150, a transmitter 152, one or more embedded orinternal antenna elements 154, 156, Local Oscillators (LOs) 158, and aprocessing module such as a Digital Signal Processor (DSP) 160.

The particular design of the communication subsystem 104 is dependentupon the network 180 in which the mobile device 100 is intended tooperate, thus it should be understood that the design illustrated inFIG. 2 serves only as one example. Signals received by the antenna 154through the network 180 are input to the receiver 150, which may performsuch common receiver functions as signal amplification, frequency downconversion, filtering, channel selection, and analog-to-digital (ND)conversion. ND conversion of a received signal allows more complexcommunication functions such as demodulation and decoding to beperformed in the DSP 160. In a similar manner, signals to be transmittedare processed, including modulation and encoding, by the DSP 160. TheseDSP-processed signals are input to the transmitter 152 fordigital-to-analog (D/A) conversion, frequency up conversion, filtering,amplification and transmission over the network 180 via the antenna 156.The DSP 160 not only processes communication signals, but also providesfor receiver and transmitter control. For example, the gains applied tocommunication signals in the receiver 150 and transmitter 180 may beadaptively controlled through automatic gain control algorithmsimplemented in the DSP 160.

The wireless link between the mobile device 100 and the network 180 maycontain one or more different channels, typically different RF channels,and associated protocols used between the mobile device 100 and thenetwork 180. An RF channel is a limited resource that must be conserved,typically due to limits in overall bandwidth and limited battery powerof the mobile device 100.

When the mobile device 100 is fully operational, the transmitter 152 istypically keyed or turned on only when it is sending to the network 180and is otherwise turned off to conserve resources. Similarly, thereceiver 150 is periodically turned off to conserve power until it isneeded to receive signals or information (if at all) during designatedtime periods.

The various embodiments described herein relate to a power managementblock that can be used in the transmitter 152 of the communicationsubsystem 104. The power management block provides improved control forthe gain control signal provided to a pre-amplifier and the supplyvoltage provided to a power amplifier. The pre-amplifier and the poweramplifier are both in a power amplification block of the transmitter152. The power expended by the power amplifier is optimized by employinga continuous control in which at least one feedback loop is employed totake into account various characteristics of certain components of thetransmitter including the pre-amplifier and the power amplifier as wellas various control signals. The structure and processing methodologyemployed by the power management block also results in constant codedomain performance, as will be explained in further detail below.

In communication systems that employ orthogonal code channels to combineand separate various streams of data, the designer must be careful notto accidentally combine, leak or add noise to the different channels bydistorting the composite signal. In most designs, the final amplifier(usually the power amplifier) is the device most likely to be driveninto non-linear operation. This is especially true when power savingtechniques are used. If the degree to which the power amplifier iscompressed varies considerably during its range of operation, it ispossible that the undesirable effects in the code domain will be presentat some power levels and not others. This makes pre-compensation of thevarious code channels impossible unless one has the means to vary thecompensation as the power demands are changed. A power amplifier withnearly constant compression will aid in the overall design of atransmitter with constant code domain performance and help simplify thebaseband design without sacrificing power efficiency.

Referring now to FIG. 3, shown therein is a block diagram of anexemplary embodiment of a portion of the transmitter 152, a duplexer 260and the antenna 156 of the communication subsystem 104. The transmitter152 includes a power management block 202, a detector 203, a coupler205, a power amplification block 204, an isolator 209 and an outputcoupler 211. The isolator 209 and the output coupler 211 are optional asis described further below. The duplexer 260 is also connected to thereceiver 150 (not shown). The power management block 202 includes apower limit control block 207, a switching regulator control block 208,a switched mode power supply 210, a compensating control block 212, anda summer 213. The power amplification block 204 includes a pre-amplifier214, and a power amplifier 216. In alternative embodiments, the outputcoupler 211 can be fed to a detector for power limiting for some cases.

It should also be noted that the power limit control block 207, thecompensating control block 212, the summer 213 and the TX_lim controlsignal 224 are optional in some embodiments. In these embodiments, theAGC signal 222 is provided as the gain control signal 230 to thepre-amplifier 214. Depending on the particular application, the powerlimit control loop and the compensating loop can be used separately.These loops are discussed in further detail below.

The wireless communications device 100 generates a data signal that isto be transmitted using the transmitter 152. The data signal istypically a comparatively low frequency signal that is generallyreferred to as a baseband signal. The baseband signal is processed byvarious components (not shown but commonly known to those skilled in theart) of the communication subsystem 104 and mixed with a carrier signalhaving a substantially higher frequency to produce a transmission signal225. The transmission signal 225 is amplified by the power amplificationblock 204 to produce an amplified transmission signal 227 for wirelesstransmission. The amplified transmission signal 227 is then sent throughthe isolator 209, the output coupler 211, and the duplexer 260 to beradiated by the antenna 156. The isolator 209 protects the poweramplification block 204 from reflections or other signal energy thatcomes from the downstream components, such as the antenna 156. Theisolator 209 can sometimes be used to stabilize the performance of theduplexer 260.

The pre-amplifier 214 is a variable gain amplifier that produces apre-amplified transmission signal 229. The gain of the pre-amplifier 214is varied to provide a first amount of gain depending on the desiredpower level for the amplified transmission signal 227. The gain of thepre-amplifier 214 is dictated by a gain control signal 230 provided bythe power limit control block 207. The power amplifier 216 thenamplifies the pre-amplified transmission signal 229 to provide theremainder of the required gain. A filter (not shown) may optionally beadded after the pre-amplifier 214 for removing noise that is introducedinto the pre-amplified transmission signal 229 by the pre-amplifier 214and prior stages of the wireless communications device 100. A personskilled in the art will be capable of selecting appropriate parametersfor this filter.

At any point during operation, the power amplifier 216 requires a supplyvoltage signal 232 with a magnitude that is sufficient so that theamplified transmission signal 227 can be produced with at most a maximumlevel of acceptable distortion. If the power amplifier 216 is alwaysoperating with the same level of acceptable distortion, then a fixedcorrection of the corresponding baseband data can be done to counteractthe distortion while saving power. Accordingly, when the amplifiedtransmission signal 227 is at any power within the transmitter's dynamicrange, the power amplifier 216 should have constant headroom to ensurethat the amplified transmission signal 227 is at most, always distortedin the same fashion.

One reason for significant power loss in the power amplification block204 is that the amplified transmission signal 227 is rarely at themaximum level mentioned above and is usually at a much lower powerlevel. The excess headroom between the supply voltage 232 provided tothe power amplifier 216 and the magnitude of the amplified transmissionsignal 227 is dissipated as heat. To avoid this power loss, the switchedmode power supply 210 is controlled by the switching regulator controlblock 208 to minimize the headroom but allow the power amplifier 216 toproduce the amplified transmission signal 227 with the instantaneousmaximum power that is required for transmission.

A trim signal 220 is a control signal that is provided to the powermanagement block 202 by the control unit 102. The trim signal 220 isused to remove unit-to-unit variation during factory calibration of thewireless communications device 100. The variation is due to offsetscaused by part variation for the components used to build thetransmitter 152 and the control loops. The trim signal 220 trims orreduces variations caused by these offsets/tolerances. This can be doneby sampling the output of the switched mode power supply 210 duringoperation and adjusting the value for the trim signal 220 to obtainacceptable performance. In addition, the compression artifacts of thetransmitter 152 can be measured and the value of the trim signal 220adjusted until the desired amount of distortion is observed. The trimsignal 220 can be optional in some designs depending on the tolerancestackup.

A detector 203 senses the pre-amplified transmission signal 229, whichis the input drive for the power amplifier 216, via a coupler 205. Thedetector 203 then produces a detected pre-amp output signal 221. In someimplementations, the detector 203 can be an approximation to a true RMSdetector with a linear scaled output. However, detectors having otherforms of output, including a log output, may also be utilized. Thelocation of the detector 203 results in loop stability and power savingsby not coupling with the output of the power amplifier 216 to sense theamplified transmission signal 227. Gain expansion of the power amplifier216 would result in a control system with right hand poles, if thedetector 203 is placed where it can be influenced by the gain expansion(i.e. on the output side of the power amplifier 216). With the detector203 at the output of the power amplifier 216, an increase in power,caused by gain expansion or maybe noise, for example, would cause thedetected output to increase and drive up the supply voltage signal 232.The resulting gain expansion would further increase the detected power.The process would then escalate. This is avoided by placing the detector203 at the output of the pre-amplifier 214.

A person skilled in the art can select the appropriate coupler 205 touse with the detector 203. This selection process will be based onparameters such as the type of power amplifier 216, tuning of thevarious control blocks in the power management block 202, and intendedoverall performance targets for the power management block 202. Adirectional coupler can be used for the coupler 205, but a resistive tapmay also be used if the pre-amplifier 214 has sufficient reverseisolation.

The detected pre-amp output signal 221 and the trim signal 220 areprovided to the power management block 202 to limit the output power ofthe amplification block 204. This is done by using these signals, aswell as other information discussed below, to perform at least one ofadjusting the gain of the pre-amplifier 214 and controlling the switchedmode power supply 210 to provide the supply voltage signal 232 at acertain level. It should be noted that the main source of variation inthe transmitter design is not due to the thermal characteristics of thepower amplifier 216 but rather the variations in the thermal andfrequency characteristics of the pre-amplifier 214, which are poor.Consequently, by detecting the output power 229 of the pre-amplifier214, most of the variation in the transmitter 152 can be removed whiledecreasing the power losses in the transmitter 152.

The switching regulator control block 208 controls the switched modepower supply 210 to provide the supply voltage signal 232 in an optimalfashion based on the trim signal 220 and the detected pre-amp outputsignal 221. The switch control block 208 applies a switching controltransfer function to the detected pre-amp output signal 221 and the trimsignal 220 to generate a switching supply control signal 228 to controlthe switched mode power supply 210. In addition, in someimplementations, it may be desirable to filter certain high frequencynoise components from the supply voltage signal 232. The switched modepower supply 210 may be a DC-DC switch converter. However, a broad classof devices may be utilized as the switched mode power supply 210 as longas the output voltage, current, efficiency and noise requirements of theamplification block 204 are met.

Through the appropriate selection of the detector 203 and values for theswitching control transfer function, the switching regulator controlblock 208 can provide control values to the switched mode power supply210 to hold the power amplifier 216 in a state of constant compression.This means that the compression artifacts of the amplified transmissionsignal 227 are maintained at a constant fraction of the actual datasignal. Consequently, power savings are optimized by minimizing thesupply voltage overhead of the power amplifier 216 at all transmissionpowers possible, and the effects of the compression of the poweramplifier 216 on the amplified transmission signal 227 becomes aconstant function of the transmission power. This is because, the poweramplifier 216 is being provided with as minimal amount of supply powerby the supply voltage signal 232, while still meeting variousspecifications such as maximum acceptable distortion, over a wide rangeof transmission power. This allows a static compensation to be appliedat the baseband rather than another compensation method that varies withtransmission power. In other words, if the compression of the poweramplifier 216 changes as a function of power, a dynamic compensation ofthe relative code domain power is required. The term code domain powerrefers to the relative power to noise ratio of the code channel inquestion (the other channels are orthogonal and appear like noise).Static compensation refers to setting the code domain correction tocompensate for the characteristics of the hardware but not for varyingpower.

The switching control transfer function is derived from acharacterization of the response of the detector 203, control curves ofthe switched mode power supply 210, and the response of the poweramplifier 216 to input drive. These values are captured by method 300.

Referring now to FIG. 4, shown therein is a flow chart diagram of anexemplary method 300 that can be used for determining appropriate valuesfor the switching control transfer function for the switching regulatorcontrol block 208. The method 300 is performed on several wirelesscommunication devices and the test results are aggregated to form theswitching control transfer function used by the switching regulatorcontrol block 208. The method 300 begins at step 302 at which thetransmitter 152 is turned on. At step 304, the amplified transmissionsignal 227 and the compression of the power amplifier 216 are observed.At step 306, the switching regulator control block 208 is overridden,and the switched mode power supply 210 is adjusted until the desiredcompression is achieved for the power amplifier 216. Step 306 sometimesjumps directly (not shown) to step 310 if the voltage adjustmentperturbs the operating power too much. The output of the detector 203(i.e. the detected pre-amp output signal 221) and the control setting ofthe switched mode power supply 210 are noted in a data table at step308. At step 310, the power of the transmitter 152 is adjusted and steps304 to 310 are repeated until enough data points are obtained.

In other words, the switching control transfer function can be generatedby looking at several different output power levels for the poweramplifier 216, and decreasing the supply voltage signal for of theselevels until an acceptable minimum level of headroom is obtained foreach power level. This provides a first relationship between the powerlevel of the power amplifier 216 and the level of the supply voltagesignal 232. These different power levels are then related to the levelof input drive (i.e. the output of the detector 203) while the supplyvoltage signal 232 is held at the minimum level just discovered for eachpower level to obtain a relationship between the level of input driveand the power level of the power amplifier 216. These two relations arethen combined to define the switching control transfer function betweenthe output of the detector 203 and the output of the switched mode powersupply 210. The step response of the switching control transfer functioncan then be observed, either through modeling or actual testing, andcertain parameters of the transfer function are adjusted to obtainacceptable timing.

The data points generated through the method 300 are then used to derivethe optimal switching control transfer function for the switchingregulator control block 208. An option at this point is to employ someinterpolation between the measured points if so desired. While themethod 300 generates static values for obtaining the switching controltransfer function of the switching regulator control block 208, themethod 300 can be modified where the transmitter power is stepped sothat dynamic characteristics are observed. At this point, an optionalcorrection can be added for the time responses of the power managementand amplification blocks 202 and 204. This can be done in eitherhardware or software. The steps to perform this are: 1) measure the stepresponse of the system, 2) analyze the shape of the response todetermine the compensation needed for the transfer functions in order tomeet timing requirements, 3) apply the compensation and test the system,and 4) go back to step one if necessary and repeat until the performanceis satisfactory. This process is fairly iterative as one sometimes findssome undesired side effects during testing. The switching controltransfer function can then be defined at this point by looking at thestep response of the power management and amplification blocks 202 and204 and generating the appropriate inverse.

The switching control transfer function employed by the switchingregulator control block 208 can be realized with hardware by using afilter with a linear, first-order low pass function and an offset. Thefilter is offset a bit to compensate for the response of theswitcher/other circuits which don't operate properly at 0 volts.Implementation as a filter can be done by taking the desired timeresponse of the switching control transfer function, applying theLaplace transform to it, then synthesizing the filter based on the polesand zeros that are generated. However, the switching control transferfunction can also be realized with software by using a look-up table.

The response time of the switching control transfer function is takeninto consideration since the time response of the entire transmitter 152is subject to regulatory requirements for the relationship between powerand time which is network dependant. As such, the response of each blockis considered since, for instance, sloppy performance in the switchedmode power supply 210 means that more compensation is needed elsewhere.Time response is also a factor when software is used to implement theswitching control transfer function. With software, the analysis is doneassuming discrete time steps. Time response for software depends in parton the guaranteed latency of the software used to do the computationsand/or lookups. On a processor with many applications runningconcurrently time response depends on: 1) code efficiency, and 2) theoperating system, which can ensure guaranteed latencies when executingreal time code. In general, the timing of the components is adjusted toprovide a best fit to the timing requirements that are stipulated by thestandard and network providers. The value for one timing parameter mayneed to be traded off against the value for another timing parameter.

The gain control signal 230 is set by the power limit control block 207based on various inputs. An automatic gain control (AGC) signal 222 anda transmit limit (TX_lim) control signal 224 are provided by the controlunit 102. Alternatively, these signals can be provided by a processor inthe communication subsystem 104 if one exists. The TX_lim control signal224 specifies the maximum allowable power of the output of the poweramplifier 216. The AGC 222 is modified by the output of the compensatingcontrol block 212. The power limit control block 207 also receives thedetected pre-amp output signal 221, and combines these signals to reducethe input drive to the power amplifier 216 by controlling the gain ofthe pre-amplifier 214. The effect of reduced input drive is a reductionin the power of the amplified transmission signal 227.

Referring now to FIG. 5, shown therein is a block diagram of anexemplary embodiment of the power limit control block 207. The powerlimit control block 207 includes a summer 402, a clipper 404, anintegrator 406, a power limiting transfer function 408, and a secondsummer 410. The power limit control block 207 can anticipate an overpower condition before it occurs and provide appropriate values for thegain control signal 230 to prevent the over power condition fromoccurring. This is based on the selection of particular values for thepower limiting transfer function 408, and by examining both the powererror signal (i.e. the output of summer 402) and the rate of change ofthe power error signal (i.e. the error signal 412) before generating newvalues for the gain control signal 230. The rate of change of thesesignals is related to the rate of change of the output of the detector203. If there is a high rate of change, there is likely to be anovershoot in the output power and an over power condition will result.

The power error signal is obtained when the summer 402 subtracts theTX_lim signal 224 from the detected pre-amp output signal 221. Thisdifference is then passed sequentially through the clipper 404, theintegrator 406, and the power limiting transfer function 408 to producethe error signal 412. The clipper 404 produces a clipped power errorsignal by converting all negative input values to zero, and passingpositive values with an adjustment factor to account for the amount ofcorrection deemed necessary to correct for the worst AGC error.Accordingly, the output of the clipper 404 is zero when the TX_limsignal 224 has a larger amplitude than the detected pre-amp outputsignal 221. Further, the output value of the clipper 404 is equal to theamplitude difference between the detected pre-amp output signal 221 andthe TX_lim signal 224 multiplied by an adjustment factor when thepre-amp output signal 221 is larger than the TX_lim signal 224. Theadjustment factor is used for scaling purposes to compensate for thesensitivity of the various components that are used. Without the clipper404, the power limit control block 242 would force the transmitter 152to run at maximum power irrespective of the value of the AGC signal 222.The integrator 406 then integrates the clipped power error signal toprovide an integrated power error signal (to achieve zero residual errorin the transmitted power when the power limit control block 207settles). The integrator 406 can be implemented in hardware or software.

The power limiting transfer function 408 has a linear term and afirst-order derivative term. The power limiting transfer function 408processes the integrated power error signal to detect an over powercondition before it occurs. During rapid ramp-up of the output power,the power control loop, including the switching regulator control block208 and the switched mode power supply 210, may not respond quicklyenough on its own. When a large rate of change of integrated error isdetected, one can assume that the limit has been exceeded and the outputsignal needs to be clamped quickly. This functionality is provided bythe various blocks in the power limit control block 207 including thepower limiting transfer function 408. The power limiting transferfunction 408 is chosen to get the desired transient performance of thepower limit control block 207. The power limiting transfer function 408also compensates for the behavior of the pre-amplifier 214 and otherdelays in the transmitter 152. This can be done by applying priorknowledge of the different shaped power ramps to the control of thetransmission power limit. The term “power ramp” refers to therelationship between power and time that is used to transition betweendifferent power levels. The knowledge of the desired shape, i.e. timeresponse, allows for a more accurate design of the power limitingtransfer function.

When the transmitter power limit TX_lim is exceeded, the error signal412 is subtracted from the modified AGC signal 223 by the summer 410 toproduce the gain control signal 230 to control the gain of thepre-amplifier 214. Alternatively, if the power limit TX_lim is notexceeded, the error signal has a value of 0 and the gain control signal230 is the modified AGC signal 223. The modified AGC signal 223 isgenerated by subtracting the output of the compensating control block212 from the AGC signal 222.

The power limiting transfer function 408 can be generated by selectingvarious values for the detected signal 221, thereby testing variouslevels of over power with respect to the value of the transmit powercontrol signal TX_lim 224, and selecting values for the transferfunction such that the level of the error signal 412 is adjusted so thatthe gain control signal 230 results in an acceptable level of inputdrive provided by the output of the pre-amplifier 214. This sets thesteady state characteristics of the power limiting transfer function408. The transient characteristics of the power limiting transferfunction 408 are then observed by looking at the step response of thepower limiting transfer function 408. The values of the power limitingtransfer function 408 are then adjusted so that the overshoot and thesettling time of the step response are acceptable. In designs thatinclude the switching control loop, the compensating loop, and the powerlimiting loop, the switching control transfer function and thecompensating transfer function are selected and tuned first beforetuning the power limiting transfer function.

Calibration difficulties come from the gain variation of the poweramplifier 216 when the magnitude of the supply voltage signal 232 ischanged. As the magnitude of the supply voltage signal 232 is increased,the gain of the power amplifier 216 also increases. In previous controlschemes, the supply voltage signal 232 was controlled as a function ofthe AGC signal 222. As the AGC signal 222 increases, the gain of thepower amplifier 216 increases predictably but the output increases muchmore rapidly at certain points in the curve. This is due to the combinedeffect of increased pre-driver gain and the gain change in the poweramplifier 216 due to the supply voltage signal 232. Accordingly, kinksin the control curve can be eliminated by applying additionalcompensation to the AGC signal 222 and providing the pre-amplifier 214with a modified gain control signal 230.

The topology shown of the power management block 204 in FIG. 3 isdesigned to address the deficiencies in conventional switcher controlschemes. The power management block 204 employs a compensating feedbackloop to create a linear relationship between the AGC signal 222 and thepower of the amplified transmission signal 227. The compensatingfeedback loop includes the compensating control block 212 and the summer213. The compensating control block 212 is an estimator that samples thesupply voltage signal 232 at the output of switched mode power supply210 and translates the supply voltage signal 232 into a gain correctionsignal 234. The gain correction signal is then subtracted from the AGCsignal 222 via the summer 213 to produce a modified gain control signal223. The compensating feedback loop acts to null the ill effectsintroduced by varying the magnitude of the supply voltage signal 232 tothe power amplifier 216.

A compensating transfer function can be used to translate a value forthe supply voltage signal 232 to a value for the gain correction signal234. First, the relationship between the gain and the supply voltagesignal 232 for the power amplifier 216 is determined for several poweramplifiers. Once an average relationship has been obtained it isinversed, taking into account some average characteristics of thepre-amplifier 214, such as the control slope of the pre-amplifier 214,to produce the compensating transfer function such that there is alinear relationship between the gain and the supply voltage signal 232.One characteristic of the pre-amplifier 214 to consider is the averagegain versus control voltage curve. The thermal characteristics can becompensated for at top power by matching the characteristics of thedetector and transmitter chain. Alternatively, another design which usesbrute force software compensation may be used that has compensation fortemperatures at all power levels. Once the compensating transferfunction is selected, the transient properties are examined by lookingat the step response to make sure that it falls within acceptablelimits. In designs which use the switching control transfer function,the compensating transfer function is selected and tuned after theswitching control transfer function has been selected and tuned. Indesigns which also use the power limiting transfer function, theparameters for the power limit control block 207 are set high to nothave an effect on selecting and tuning the compensating transferfunction.

The compensating transfer function may be implemented in software by alookup table or in hardware using a hardware filter. When thecompensating transfer function is realized via a lookup table, thesupply voltage signal 232 and its rate of change is used to determine avalue for the gain correction signal 234. The rate of change of thesupply voltage signal 232 can be used to anticipate the state that thepower amplifier 216 will be in next because it takes some time for theother circuits to adjust. In a more advanced design one can monitorother bias parameters.

When the compensating transfer function is realized with a filter, theLaplace transform is applied to the time response or impulse responsethat corresponds to the compensating transfer function, and the filteris then synthesized based on the poles and zeros that are generated bythe Laplace transform operation. The selection of the compensatingtransfer function allows for compensation not only of static gainchanges but also dynamic variation due to lags in the power managementcontrol and power amplification blocks 202 and 204. The compensatingtransfer function has a linear term and a first order derivative term.

The effect of the compensating feedback loop is to linearize therelationship between the power of the amplified transmission signal 227and the AGC signal 222 for the transmitter 152. Another result is thatthe compensating feedback loop decreases or postpones saturation effectsfor this relationship. Also, separating the power limiting function fromthe compensating control function decreases the accuracy requirements ofthe compensating control block 212.

It should be noted that accurate, data rate independent power limitingis provided by the choice of the detector 203 and the way that the powerlimit control block 207 is tuned. As the peak to average power ratiochanges, the observed output of the detector 203 varies if it is not atrue RMS detector. The accuracy of the power limiting transfer function408 will depend on detecting true RMS power. Also, some detectors willhave a log output. With a log output, the top part of the scale is morecompressed so fine control of the output power involves comparingincreasingly smaller voltage differences. With a linear true RMSdetector, the measurement is data rate independent and the top end ofthe scale is expanded. However, in some designs, a non-RMS detector canbe used.

As with the switching control transfer function, the power limitingtransfer function 408 and the compensating control transfer function canbe implemented in hardware with a filter. Alternatively, these transferfunctions may be implemented with software (i.e. as a look-up table).

By placing the detector 203 after the pre-amplifier 214 and before thepower amplifier 216, it is possible to eliminate the isolator 209 andoutput coupler 211. In contrast, if the detector 203 was placed at theoutput of the power amplifier 216, the isolator 209 and/or outputcoupler 211 would be required to prevent reflected power from beingsensed by the detector 203. Further, there would be power losses in theamplified transmission signal 227 due to the sampling done by thecoupler 205 if it was placed at the output of the power amplifier 216.

The isolator 209 and the output coupler 211 can be removed since thereverse isolation of the power amplifier 216 prevents reflected powerfrom reaching the detector 203. The reverse isolation of the poweramplifier 216 is indicated by the S₁₂ parameter which is the ratio ofthe power at the input of the power amplifier 216 to the power at theoutput of the power amplifier 216 when no input signal is provided tothe power amplifier 216 and power is injected at the output of the poweramplifier 216. A good reverse isolation can be achieved by controllingthe drain gate capacitance of the final gain stage of the poweramplifier 216 (for FET power amplifiers) or the collector basecapacitance of the final gain stage of the power amplifier 216 (for HBTpower amplifiers).

The removal of the isolator 209 and the output coupler 211 results in acost/space savings due to implementing the transmitter 152 with areduced number of components. In addition, the removal of the isolator209 and the output coupler 211 eliminates additional components wherepower may be diverted or dissipated between the power amplificationblock 204 and the antenna 156, which reduces the amount of power loss inthe amplified transmission signal 227 before it reaches the antenna 156.

However, with removal of the isolator 209 and the output coupler 211,the power amplifier 216 must be matched to the duplexer 260 to preventload-induced power changes (especially if the isolator 209 is removed).Reflected power at the output of the power amplifier 216 as a result ofload shifts can cause the forward power to change by upsetting theoperating point of the power amplifier 216. Also, the reflected powercan sometimes disturb the input of the power amplifier 216 if thereverse isolation is poor. However, with good reverse isolation andmatching to the duplexer 260, the isolator 209 and the output coupler211 can be removed without incurring the usual maximum output poweraccuracy penalties.

It should be noted that the architecture of the power management block202 along with the location of the detector 203 results in: 1) accurate,rate independent power limiting (due to a combination of the powerlimiting transfer function 408 and the detector choice resulting in anexpanded upper range), 2) linearization of the AGC curve versustransmission power for the amplification block 204, and 3) almostconstant power amplifier compression versus transmitter power. Further,each transfer function is tuned in an appropriate manner related to itsfunctionality and the transfer functions used in the various blocks aredifferent from one another.

The structure and method described herein allow for the operation of thepower amplifier 216 in constant compression independent of the power ofthe transmitter 152. This results in: a) optimal power savings since thepower amplifier 216 is provided with a minimum of supply voltage asdescribed previously, and b) constant code domain performance. Thearchitecture of the transmitter 152 also allows for lower losses betweenthe power amplifier 216 and the antenna 156 without incurring poweraccuracy penalties.

The power management block 204 can be divided into three subcomponents:a switching regulator control loop, a compensating feedback loop and apower limiting feedback loop. The switching regulator control loopincludes the coupler 205, the detector 203, the switching regulatorcontrol block 208, and the switched mode power supply 210. Thecompensating feedback loop includes the components of the switchingregulator control loop as well as the compensating control block 212,and the summer 213 and receives inputs from the AGC control signal 222and the TX_lim control signal 224. The power limiting feedback loopincludes the coupler 205, the detector 203, and the power limit controlblock 207 and receives inputs from the output of the summer 213 and theTX_lim control signal 224.

In one aspect, at least one embodiment described herein provides atransmitter for a wireless communications device. The transmittercomprises a power amplification block comprising a pre-amplifierconfigured to amplify a transmission signal to produce a pre-amplifiedtransmission signal; and a power amplifier coupled to the pre-amplifierand configured to amplify the pre-amplified transmission signal toproduce an amplified transmission signal. The transmitter furthercomprises a detector coupled to the output of the pre-amplifier andconfigured to provide a detected pre-amp output signal; and a powermanagement block. The power management block comprises a switchingregulator control block configured to generate a switching supplycontrol signal based on the detected pre-amp output signal; and aswitched mode power supply coupled to the switching regulator controlblock and configured to generate a supply voltage signal based on theswitching supply control signal and provide the supply voltage signal tothe power amplifier.

In another aspect, at least one embodiment described herein provides amobile communication device comprising a main processor configured tocontrol the operation of the mobile communication device; and acommunication subsystem connected to the main processor, thecommunication subsystem being configured to send and receive data. Thecommunication subsystem comprises a power amplification block, adetector, and a power management block. The power amplification blockcomprises a pre-amplifier configured to amplify a transmission signal toproduce a pre-amplified transmission signal; and a power amplifiercoupled to the pre-amplifier and configured to amplify the pre-amplifiedtransmission signal to produce an amplified transmission signal. Thedetector is coupled to the output of the pre-amplifier and configured toprovide a detected pre-amp output signal. The power management blockcomprises a switching regulator control block configured to generate aswitching supply control signal based on the detected pre-amp outputsignal; and a switched mode power supply coupled to the switchingregulator control block and configured to generate a supply voltagesignal based on the switching supply control signal and provide thesupply voltage signal to the power amplifier.

In yet another aspect, at least one embodiment described herein providesa method of providing a switching supply control signal to a poweramplification block of a transmitter, the power amplification blockincluding a pre-amplifier and a power amplifier. The method comprisesdetecting the output of the pre-amplifier to provide a detected pre-ampoutput signal; generating a switching supply control signal based on thedetected pre-amp output signal; and generating the supply voltage signalby providing the switching supply control signal to a switched modepower supply.

Various embodiments have been described herein by way of example only.Various modification and variations may be made to these embodimentswithout departing from the spirit and scope of these embodiments, whichis defined by the appended claims.

1. A control system for a transmitter of a wireless device, thetransmitter having a pre-amplifier and a power amplifier coupled to anoutput of the pre-amplifier, the control system comprising: a signalinput for receiving a detection signal representative of a pre-amplifiedtransmission signal sensed at the output of the pre-amplifier by adetector; a switching regulator control block configured to generate aswitching supply control signal based on the received detection signal,the switching supply control signal comprising control values for aswitched mode power supply configured to generate a supply voltagesignal for the power amplifier in response to the switching supplycontrol signal; a power limit control block configured to generate again control signal based on an automatic gain control signal related tothe pre-amplifier, the received detection signal, and a transmit powerlimit signal for limiting transmission power of the transmitter, thegain control signal being provided to the pre-amplifier for controllinggain in the pre-amplifier; and a signal output for providing theswitching supply control signal to the switched mode power supply;wherein, in operation, the switching regulator control blockcommunicates with the detector using the signal input and with theswitched mode power supply using the signal output.
 2. The controlsystem of claim 1, wherein the switching regulator control block isconfigured to generate the switching supply control signal by applying aswitching control transfer function to the received detection signal,the switching control transfer function having values determined basedon a characterization of the response of the detector, control curves ofthe switched mode power supply, and a response of the power amplifier toinput drive.
 3. The control system of claim 2, wherein the switchingregulator control block is configured to generate the switching supplycontrol signal further based on a trim signal generated to compensatefor component tolerances.
 4. The control system of claim 1, wherein theswitching regulator control block is implemented with a processor andthe switching control transfer function is defined using one or morelook-up tables.
 5. The control system of claim 1, wherein the powerlimit control block is implemented with a processor and is configured toapply a power limiting transfer function defined using one or morelook-up tables to generate the gain control signal.
 6. The controlsystem of claim 1, wherein the control values for the switched modepower supply are generated to hold the power amplifier in a state ofconstant compression.
 7. The control system of claim 1, wherein thepower management block further comprises a compensation control blockconfigured to provide a gain correction signal based on the supplyvoltage signal, and wherein the gain correction signal is subtractedfrom the automatic gain control prior to providing the automatic gaincontrol signal to the power limit control block.
 8. A method ofcontrolling a transmitter of a wireless device, the transmitter having apre-amplifier and a power amplifier coupled to an output of thepre-amplifier, the method comprising: receiving a detection signalrepresentative of a pre-amplified transmission signal sensed at theoutput of the pre-amplifier by a detector; generating a switching supplycontrol signal based on the received detection signal, the switchingsupply control signal comprising control values for a switched modepower supply configured to generate a supply voltage signal for thepower amplifier in response to the switching supply control signal;generating a gain control signal based on an automatic gain controlsignal related to the pre-amplifier, the received detection signal, anda transmit power limit signal for limiting transmission power of thetransmitter, the gain control signal being provided to the pre-amplifierfor controlling gain in the pre-amplifier; and providing the switchingsupply control signal to the switched mode power supply.
 9. The methodof claim 8, further comprising generating the switching supply controlsignal by applying a switching control transfer function to the receiveddetection signal, the switching control transfer function having valuesdetermined based on a characterization of the response of the detector,control curves of the switched mode power supply, and a response of thepower amplifier to input drive.
 10. The method of claim 9, furthercomprising generating the switching supply control signal based on atrim signal generated to compensate for component tolerances.
 11. Themethod of claim 8, wherein the switching supply control signal isgenerated by a processor and the switching control transfer function isdefined in using one or more look-up tables.
 12. The method of claim 8,wherein the gain control signal is generated by a processor, and themethod further comprises applying a power limiting transfer functionusing one or more look-up tables to generate the gain control signal.13. The method of claim 8, further comprising generating the controlvalues for the switched mode power supply to hold the power amplifier ina state of constant compression.
 14. The method of claim 8, furthercomprising generating a gain correction signal based on the supplyvoltage signal, and wherein the gain correction signal is subtractedfrom the automatic gain control signal prior to generating the gaincontrol signal.
 15. A non-transitory computer-readable storage mediumstoring instructions executable by a processor coupled to the storagemedium, the instructions, when executed by the processor, cause theprocessor to perform acts of a method of controlling a transmitter of awireless device, the transmitter having a pre-amplifier and a poweramplifier coupled to an output of the pre-amplifier, said actscomprising: receiving a detection signal representative of apre-amplified transmission signal sensed at the output of thepre-amplifier by a detector; generating a switching supply controlsignal based on the received detection signal, the switching supplycontrol signal comprising control values for a switched mode powersupply configured to generate a supply voltage signal for the poweramplifier in response to the switching supply control signal; generatinga gain control signal based on an automatic gain control signal relatedto the pre-amplifier, the received detection signal, and a transmitpower limit signal for limiting transmission power of the transmitter,the gain control signal being provided to the pre-amplifier forcontrolling gain in the pre-amplifier; and providing the switchingsupply control signal to the switched mode power supply.
 16. Thenon-transitory computer-readable storage medium of claim 15, whereinsaid acts further comprise generating the switching supply controlsignal by applying a switching control transfer function to the receiveddetection signal, the switching control transfer function having valuesdetermined based on a characterization of the response of the detector,control curves of the switched mode power supply, and a response of thepower amplifier to input drive.
 17. The non-transitory computer-readablestorage medium of claim 16, wherein said acts further comprisegenerating the switching supply control signal based on a trim signalgenerated to compensate for component tolerances.
 18. The non-transitorycomputer-readable storage medium of claim 15, wherein said acts furthercomprise defining the switching control transfer function using one ormore look-up tables.
 19. The non-transitory computer-readable storagemedium of claim 15, wherein said acts further comprise applying a powerlimiting transfer function using one or more look-up tables to generatethe gain control signal.
 20. The non-transitory computer-readablestorage medium of claim 15, wherein said acts further comprisegenerating the control values for the switched mode power supply to holdthe power amplifier in a state of constant compression.
 21. Thenon-transitory computer-readable storage medium of claim 15, whereinsaid acts further comprise generating a gain correction signal based onthe supply voltage signal, and wherein the gain correction signal issubtracted from the automatic gain control signal prior to generatingthe gain control signal.